As a method for manufacturing a lithium ion secondary battery, for example, Patent Literature 1 discloses the following: a slurry in which a conductive agent and a binding agent are dispersed in a solvent is coated onto a collector; then, the conductive agent is oriented by a magnetic field, and the solvent is removed by drying; as a result, a positive electrode is manufactured. In this literature, the conductive agent is a flake graphite powder or a vapor-grown carbon fiber. Patent Literature 1 has an object of providing a battery using a positive electrode capable of exhibiting a sufficient conductivity while minimizing the amount of the conductive agent to be added.
In addition, for example, the following facts are disclosed. A flake graphite powder has an anisotropy in resistance in each particle, and the electric resistivity in the in-plane direction of a (002) layer plane is about 1000 times the electric resistivity in the plane direction. When the layer plane of the flake graphite powder can be oriented perpendicularly with respect to the collector, the current collecting efficiency can be increased. This can reduce the amount of the conductive agent to be added. Further, a flat-panel-like flake graphite has a property of tending to be oriented in parallel with the plane of the collector when coated as a slurry on the collector. When immediately after the formation of a coating film from the slurry, a magnetic field is applied to the coating film, the flake graphite can be oriented. Also for a vapor-deposited carbon fiber, the resistance is lower in the direction of the fiber length. Similarly, by orienting the fiber length direction in the direction perpendicular to the plane of the collector, high current collecting capability can be exerted with a small amount of the conductive agent. When the conductive agent is oriented in a direction perpendicular to the collector, the resistance between the collector and the reaction layer is less likely to increase even when the cycle is repeated.
In Patent Literature 2, a substance obtained by making the flake natural graphite as described above spherical is used as a negative electrode active material. Then, to the graphite particles made spherical, a binding agent is added. A thickener is mixed therein, and the mixture is water dispersed, resulting in a paste form (slurry). Then, the slurry is coated to the negative electrode collector. Then, immediately thereafter, the negative electrode collector coated with the slurry of the negative electrode mixture is allowed to stand still or to pass in a magnetic field. As a result, the graphite particles are magnetically oriented. At this step, it is considered preferable that the magnetic lines of force be applied perpendicularly and evenly with respect to the plane of the electrode. Further, it is considered preferable that the electrode be dried immediately after the magnetic orientation. Further, as the binding agent, styrene-butadiene rubber (SBR) is disclosed.
Patent Literature 3 discloses that foreign matters deposited on a positive electrode plate or a negative electrode plate are continuously removed by a magnetic means.